Internal combustion engine system and a method for an internal combustion system

ABSTRACT

An internal combustion engine system includes at least one combustor, and a first expander arranged to receive exhaust gases from at least one of the at least one combustor, and to expand and extract energy from the exhaust gases, wherein the system includes a second expander arranged to receive exhaust gases from the first expander, and to expand and extract energy from the exhaust gases.

BACKGROUND AND SUMMARY

The invention relates to an internal combustion engine system, acombined compressor and expander for an internal combustion enginesystem, a method for an internal combustion engine system, a computerprogram, a computer readable medium, and a control unit.

The invention can be applied in heavy-duty vehicles, such as trucks,buses and construction equipment, e.g. working machines. The inventioncan also be applied to cars. Although, the invention will be describedwith respect to a truck, the invention is not restricted to thisparticular vehicle type.

It is known that internal combustion engines with two stages ofcompression and two stages of expansion, e.g. by a compressor, acombustor and an expander, may provide for reaching very high pressuresand for extracting more energy from the fuel. However, a highlyefficient vehicle engine may have very cool tailpipe exhaust, which mayprevent or reduce the efficiency of exhaust treatment processes providedby exhaust treatment devices such as catalytic converters of varioustypes. For certain processes, e.g. selective catalytic reduction SCR),it is possible to compensate for low temperatures by providing largeexhaust treatment devices; however, this will increase the weight andvolume of the engine system, which may be a problem, particularly invehicles, where often there are demanding space requirements.

US2010300385 discloses an engine with two stages of compression and twostages of expansion, where an oxidation catalyst is positioned between apower cylinder and an expander cylinder. However, for many exhausttreatment processes, e.g. SCR, such a location provides temperatureswhich are too high.

It is desirable to reduce emissions from an internal combustion enginewith a compressor, a combustor and an expander. It is also desirable toprovide an internal combustion engine system with a compressor, acombustor and an expander, which provides an effective treatment ofexhaust gases, while avoiding large increases of the volume and/orweight of the engine system.

According to an aspect of the invention, an internal combustion enginesystem is provided comprising

-   at least one combustor, and-   a first expander arranged to receive exhaust gases from at least one    of the at least one combustor, and to expand and extract energy from    the exhaust gases,-   characterized in that the system comprises a second expander    arranged to receive exhaust gases from the first expander, and to    expand and extract energy from the exhaust gases.

Herein, the engine system is understood as comprising an internalcombustion engine, in turn comprising the combustor, the first expanderand the second expender.

The invention provides for the expansion of the engine system being donein at least three steps. In turn this provides for providing twodifferent temperature ranges, one upstream of the first expander, andone between the first and second expanders. Thereby the engine systemmay provide a plurality of simultaneous temperature ranges, eachsuitable for one or more respective exhaust treatment processes.

Thus, the system may advantageously be provided with an exhausttreatment device arranged to receive exhaust gases from the firstexpander, to process the received exhaust gases, and to deliver theprocessed exhaust gases to the second expander. Thereby, it is possibleto provide the exhaust treatment device in a form, e.g. as a selectivecatalytic reduction (SCR) catalyst, requiring a temperature range whichis lower than the temperature range upstream of the first expander. Inparticular, the temperature range between the expanders may be kepthigher than in a portion of an exhaust system communicating directlywith the atmosphere, e.g. a vehicle tail pipe; however, the temperaturerange between the expanders may be kept lower than between the combustorand the first expander.

In a vehicle, where the exhaust treatment device is an SCR catalyst, theposition in the elevated temperature between the expanders allows for asmaller SCR than if it would be positioned in the tailpipe. This makesit possible to provide the SCR catalyst as a cheap catalyst for nitrogenoxide (NOx) reduction in a temperature range 300-450 C with a highconversion. Specifically, the catalyst size may be reduced, whichreduces the volume and weight of the engine system.

Advantageously, the system comprises an injector arranged to injectreductant for the exhaust treatment device, upstream of the firstexpander or into the first expander. Thereby, the timing and/or durationof the reductant injections by the injector may be coordinated with theactuation of an inlet valve of the first expander. This will providegood mixing of the reductant with the exhaust gases. It is understoodthat the reductant may be a solution of urea or another reductant usefulfor lowering particulant emissions and/or nitrogen oxide emissions fromthe engine. The reductant may a solution of organic and inorganicnitrogen compounds.

As also discussed below, where the reductant comprises urea, the firstexpander may promote thermolysis of the urea to decompose it intoisocyanate and ammonia before it reaches the SCR catalyst. Thereupon theisocyanate may be processed by hydrolysis to provide ammonia. Injectingthe reductant upstream of the first expander or into the first expandermay support the thermolysis and the hydrolysis, since these processeswill be enhanced by the heat therein. Advantageously, where the firstexpander is a piston expander, the injector may be arranged to injectreductant for the exhaust treatment device, into the first expander andonto the piston of the first expander, e.g. onto a piston crown of thepiston. Thereby, the thermolysis and the hydrolysis may be particularlysupported by heat stored in the piston, e.g. in a top section of thepiston. For example, the heat stored in the piston crown of the pistonmay support the thermolysis and the hydrolysis.

Preferably, the system comprises in addition to said exhaust treatmentdevice a pre-expander exhaust treatment device arranged to receiveexhaust gases from the combustor, to provide an exhaust treatmentprocess to the exhaust gases, and to deliver processed exhaust gases tothe first expander. The pre-expander exhaust treatment device maycomprise an oxidation catalyst, and/or a particulate filter. Where bothare provided, the particulate filter may be located downstream of theoxidation catalyst. The system may further be arranged so that during anoperation thereof, the pre-expander exhaust treatment device presents atemperature within the range of 550-1300° C., preferably within therange of 550-1100° C., e.g., within the range of 550-800° C. Thepre-expander exhaust treatment device temperature may vary depending ofthe engine load. At full engine load, the pre-expander exhaust treatmentdevice temperature may be e.g. 900-1100° C. Thereby, an advantageousdistribution of exhaust treatment devices along the path of the exhaustgases may be provided, giving different temperatures which are eachoptimized for the respective exhaust treatment device.

It is understood that depending on the provision of the pre-expanderexhaust treatment device, the first expander is arranged to receiveprocessed or unprocessed exhaust gases from the combustor. Exhaust gasesare herein understood as being processed if they are received from anexhaust treatment device.

In some embodiments, e.g. where there is no pre-expander exhausttreatment device, the first expander may be arranged to utilize pressurepulses in the exhaust gases received from the at least one of the atleast one combustor, to increase the power output of the first expander.

Herein, the engine system is understood as comprising the engine, inturn comprising the combustor, the first expander and the secondexpender, and the engine system is understood as comprising the engine,and, where provided, the pre-expander exhaust treatment device, and thepost-expander exhaust treatment device.

The invention is particularly advantageous where the system comprises acrankshaft, and the combustor comprises a piston arranged to reciprocatein a cylinder, and to drive the crankshaft. It is understood that thesystem may comprise a plurality of combustors, each comprising a pistonarranged to reciprocate in a respective cylinder, whereby the pistonsare all arranged to drive the crankshaft.

The first expander is preferably a piston expander arranged to drive thecrankshaft with the extracted energy. Similarly, the second expander ispreferably a piston expander arranged to drive the crankshaft with theextracted energy. The system may comprise at least one compressor, whichmay be a piston compressor, arranged to be driven by the crankshaft.Thus, the invention may be advantageously implemented in a multistagecompression and expansion engine where the compressor(s) and theexpanders are connected to the crankshaft. Such a connection may bedirect or indirect, as exemplified below. Thereby, the system maypresent a high efficiency. Typically, the expanders may provide 30-50%,e.g. 40%, of the total power of the engine, and the compressor(s) maytake 10-20% of the total power of the engine.

It should be noted however that within the scope of the claims, thefirst expander may be of a type other than a piston expander. Forexample, the first expander may be a turbine. The turbine may bearranged to drive a compressor for compressing air for the combustor, orit may be arranged to drive the crankshaft with the extracted energy.Similarly, the second expander may be of a type other than a pistonexpander. For example, the second expander may be a turbine. The turbinemay be arranged to drive a compressor for compressing air for thecombustor, or it may be arranged to drive the crankshaft with theextracted energy.

In some embodiments, where the system comprises a compressor arranged tocompress air for at least one of the at least one combustor, the secondexpander may comprise a turbine arranged to drive the compressor or anadditional compressor. Thereby, the system may be provided with a highpower density. Where an additional compressor is provided, it may bearranged to deliver compressed air to said compressor arranged tocompress air for at least one of the at least one combustor. Thus, anadvantageous three step compression may be provided.

In an advantageous embodiment, where the system comprises a crankshaft,and a compressor arranged to compress air for at least one of the atleast one combustor, the compressor and one of the first expander andthe second expander are integrated so as to share a piston which isconnected to the crankshaft. Thereby, the compressor and the one of thefirst expander and the second expander may form a combined compressorand expander whereby the piston is arranged to reciprocate in a sharedcylinder, the combined compressor and expander being arranged to admitair to the shared cylinder, on a first side of the piston, and tocompress the air, by means of the piston, for the combustor, thecombined compressor and expander further being adapted to admit theexhaust gases, received by the one of the first expander and the secondexpander, to the shared cylinder, on a second side of the piston, toexpand the exhaust gases by means of the piston.

The shared piston makes it possible to use the urge of the piston by theexpander to deliver, in addition to power to the crankshaft, power forthe air compression in a direct manner. More specifically, the exhaustgases may provide a direct pressure on the shared piston in turn servingto directly exert a direct pressure on the air. Thereby, mechanicallosses for the transfer of this energy is substantially eliminated.Also, compared to providing the compressor and expander separately, thecompressor and expander combination results in a reduced number ofparts, since the piston and the cylinder are shared, thereby reducingthe volume, weight, complexity and cost of the engine system.

Preferably, the combustor comprises an exhaust valve, herein alsoreferred to as an outlet valve, the system further comprising a variablevalve timing mechanism arranged to actuate the exhaust valve.

Preferably, the first expander comprises an expander inlet valve, thesystem further comprising an expander variable valve timing mechanismarranged to actuate the expander inlet valve. Thereby a possibility isprovided to advantageously adjust the swallowing capacity of the firstexpander as exemplified below. For example, adjusting the temperature ofan exhaust treatment device arranged to receive exhaust gases from thefirst expander, to process the received exhaust gases, and to deliverthe processed exhaust gases to the second expander, may be done byadjusting the swallowing capacity of the first expander.

In some embodiments, the first expander is a variable-geometry turbine,e.g. of a variable-geometry turbocharger (VGT). This provides analternative possibility to adjust the swallowing capacity of the firstexpander.

Preferably, the first expander comprises an expander exhaust valve,herein also referred to as an outlet valve, the system furthercomprising an expander variable valve timing mechanism arranged toactuate the expander exhaust valve. As exemplified below, this allowsfor an advantageous manner of controlling the temperature of thepost-expander exhaust treatment device. For example, thereby the firstexpander may be used for increasing the temperature, e.g. at a coldstart event, of an exhaust treatment device arranged to receive exhaustgases from the first expander, to process the received exhaust gases,and to deliver the processed exhaust gases to the second expander. Forexample, by advancing an opening event of the expander exhaust valve, sothat it opens before a bottom dead center (BDC) position of the pistonin the first expander, the expander exhaust valve may be opened beforethe expansion in the first expander is completed. Thereby, heatremaining in the gases in the first expander may be used to increase theexhaust treatment device temperature. In addition, the exhaust valve maybe closed at the BDC position, and opened at a position after the BDCposition, e.g. 45 crankshaft degrees after the BDC position. Thereby, arecompression of the gases in the first expander may occur, and the heatgenerated thereby may be used to increase the exhaust treatment devicetemperature.

In some embodiments, the first expander may comprise a hydrolysingreactor. This is particularly advantageous where the system comprises,as described above, an injector arranged to inject reductant for anexhaust treatment device, upstream of the first expander or into thefirst expander. Where the reductant comprises urea, e.g. where theexhaust treatment device is an SCR catalyst, the first expander maypromote thermolysis of the urea to decompose it into isocyanate andammonia before it reaches the catalyst. Thereupon the isocyanate may beprocessed by hydrolysis to provide ammonia. Injecting the reductantupstream of the first expander or into the first expander may supportthe thermolysis and the hydrolysis, since these processes will beenhanced by the heat therein. The hydrolysing reactor may involve asdiscussed above an injector arranged to inject reductant for an exhausttreatment device, into the first expander and onto a piston of the firstexpander. The first expander may also provide a beneficial thoroughmixing of the reductant with the exhaust gases.

It should be noted that in some embodiments, an injector may be arrangedto inject reductant downstream of the first expander. Thereby, anexhaust treatment device such as an SCR catalyst may be provideddownstream of the second expander. This may provide a relatively longflow path for the reductant, past the second expander, to allow a goodmix of the reductant and the exhaust gases.

According to another aspect of the invention, an internal combustionengine system is provided comprising

-   at least one combustor, and-   an expander arranged to receive exhaust gases from at least one of    the at least one combustor, and to expand and extract energy from    the exhaust gases,-   characterized in that the system comprises an exhaust treatment    device arranged to receive exhaust gases from the expander, and to    process the received exhaust gases,-   and that the system comprises an injector arranged to inject    reductant for the exhaust treatment device, upstream of the expander    or into the expander.

The exhaust treatment device may be a selective catalytic reduction(SCR) catalyst. Thereby, by injecting reductant upstream of the expanderor into the expander, advantage may be taken of a higher temperature ofthe exhaust gases before they are subjected to the expansion of theexpander, to provide thermolysis of the reductant, e.g. where thereductant is provided in the form of urea, to provide ammonia for theprocess in the exhaust treatment device. In addition, such a systemallows for the expander to form a mixing volume for the reductant, whichin turn allows for reducing the volume downstream of the expander.Thereby, space can be saved which may be critical in a vehicleapplication.

Preferably, the injector is arranged to inject reductant for the exhausttreatment device, into the expander and onto a piston of the expander.Advantages thereof have been mentioned above.

The invention also provides a combined compressor and expander for aninternal combustion engine system, comprising

-   a cylinder,-   a piston adapted to be connected to a crankshaft of the engine    system, and arranged to reciprocate in the cylinder, the combined    compressor and expander being adapted to admit air to the cylinder,    on a first side of the piston, and to compress the air by means of    the piston for a combustion process of the engine system,-   the combined compressor and expander further being adapted to admit    exhaust gases, obtained from a combustion process of the engine    system and/or an exhaust gas treatment process of the engine system,    to the cylinder, on a second side of the piston, to expand the    exhaust gases by means of the piston to extract, energy from the    expanded exhaust gases.

Thereby the compressor and expander are integrated with each other, andone cylinder and piston combination may be used for both compression andexpansion. The power extracted by the expander will contribute todriving the crankshaft and/or to compress the air. The air compressionprocess may be driven by the crankshaft and/or the exhaust gasexpansion. As mentioned, the compressor and expander combination resultsin a reduced number of parts, since the piston and the cylinder areshared, thereby reducing the volume, weight, complexity and cost of theengine system.

According to another aspect of the invention, a method for an internalcombustion engine system is provided comprising

-   at least one combustor, arranged to combust air and fuel,-   a first expander arranged to receive exhaust gases from at least one    of the at least one combustor, and to expand and extract energy from    the exhaust gases,-   a second expander arranged to receive exhaust gases from the first    expander, and to expand and extract energy from the exhaust gases,    and-   an exhaust treatment device arranged to receive exhaust gases from    the first expander, to process the received exhaust gases, and to    deliver the processed exhaust gases to the second expander, the    method comprising adjusting the swallowing capacity of the first    expander to control the temperature of the process in the exhaust    treatment device.

The swallowing capacity of the first expander is understood as thecapacity of the first expander to accept gases and pass them on to aconduit downstream of the expander. The swallowing capacity of the firstexpander is proportional to the mass flow through the first expander ata given intake pressure and temperature. A decreased swallowing capacityprovides an increased strangulation of the gas flow. A decreasedswallowing capacity of the first expander provides an increased pressuredrop across the first expander. A decreased swallowing capacity mayprovide an increased first expander expansion ratio as understood by thepressure drop across the first expander.

By said method, an advantageous and reliable manner of controlling thetemperature of the process in the exhaust treatment device is provided.For example, the method may comprise increasing the temperature of theexhaust treatment device by increasing the swallowing capacity of thefirst expander, and decreasing the temperature of the exhaust treatmentdevice by decreasing the swallowing capacity of the first expander.

The first expander may be arranged to receive the exhaust gases by meansof an expander inlet valve, an expander variable valve actuationmechanism being arranged to actuate the expander inlet valve, whereinadjusting the swallowing capacity of the first expander comprisesadjusting the expander variable valve actuation mechanism. Thereby, thetemperature control may be effected by means of readily availableassemblies. The expander variable valve actuation mechanism may be e.g.a variable valve timing mechanism. The expander variable valve actuationmechanism may be of any suitable type, e.g. involving cam switching, camphasing, an oscillating cam, an eccentric cam drive, a three-dimensionalcam lobe, a two shaft combined cam lobe profile, a coaxial two shaftcombined cam lobe profile, a helical camshaft, or a camless mechanism.

The method may comprise increasing the swallowing capacity of the firstexpander by delaying a closing event of the expander inlet valve, anddecreasing the swallowing capacity of the first expander by advancingthe closing event of the expander inlet valve. For example, in twostroke cycles of the first expander, the expander inlet valve may becontrolled so as to open at a top dead center (TDC) position of thepiston in the first expander, and so as to close at 25 crankshaftdegrees after the TDC position. The swallowing capacity may be increasedby delaying the inlet valve closing, e.g. to 30 crankshaft degrees afterthe TDC position. The swallowing capacity may be decreased by advancingthe inlet valve closing, e.g. to 20 crankshaft degrees after the TDCposition.

Preferably, the first expander is arranged to expel the exhaust gases bymeans of an expander exhaust valve, the expander variable valveactuation mechanism being arranged to actuate the expander exhaustvalve, the method comprising controlling the expander variable valveactuation mechanism so as to adjust the expander exhaust valve tominimize the pressure difference across the expander exhaust valve at anopening event of the expander exhaust valve, and/or to minimize thepressure difference across the expander inlet valve at an opening eventof the expander inlet valve. The adjustment of the expander exhaustvalve to minimize the pressure difference across the expander inletvalve at an opening event of the expander inlet valve may be done bysuitable control of an expander exhaust valve closing event, to providea degree of recompression in the expander.

According to another aspect of the invention, a method for an internalcombustion engine system is provided comprising

-   at least one combustor, arranged to combust air and fuel,-   a first expander arranged to receive exhaust gases from at least one    of the at least one combustor, and to expand and extract energy from    the exhaust gases,-   a second expander arranged to receive exhaust gases from the first    expander, and to expand and extract energy from the exhaust gases,    and-   an exhaust treatment device arranged to receive exhaust gases from    the first expander, to process the received exhaust gases, and to    deliver the processed exhaust gases to the second expander, the    method comprising adjusting the swallowing capacity of the second    expander to control the temperature of the process in the exhaust    treatment device.

Similarly to the first expander, the swallowing capacity of the secondexpander is understood as the capacity of the second expander to acceptgases and pass them on to a conduit downstream of the second expander.The swallowing capacity of the second expander is proportional to themass flow through the second expander at a given intake pressure andtemperature. A decreased swallowing capacity provides an increasedstrangulation of the gas flow. A decreased swallowing capacity of thesecond expander provides an increased pressure drop across the secondexpander. A decreased swallowing capacity may provide an increasedsecond expander expansion ratio as understood by the pressure dropacross the second expander.

Thereby, a further advantageous manner of controlling the exhausttreatment device temperature is provided. Increasing the temperature ofthe exhaust treatment device may be done by decreasing the swallowingcapacity of the second expander, and decreasing the temperature of theexhaust treatment device may be done by increasing the swallowingcapacity of the second expander.

Adjusting the swallowing capacity of the first expander and/or thesecond expander may advantageously be done in dependence on a rotationalspeed of the engine system and/or a requested torque for the enginesystem. For example, with a decreasing rotational speed of the enginesystem, the swallowing capacity of the first expander may be increased,and/or the swallowing capacity of the second expander may be decreased.As another example, with an increasing requested torque, providing anincreased exhaust gas temperature, the swallowing capacity of the firstexpander may be decreased and/or the swallowing capacity of the secondexpander may be increased.

Preferably, the method comprises increasing the temperature of theexhaust treatment device by increasing the swallowing capacity of thefirst expander and decreasing the swallowing capacity of the secondexpander, and decreasing the temperature of the exhaust treatment deviceby decreasing the swallowing capacity of the first expander andincreasing the swallowing capacity of the second expander. Thereby, aparticularly effective temperature control is provided by combinedadjustments of the first and second expander swallowing capacities.However, in some embodiments, the temperature of the exhaust treatmentdevice is adjusted by adjusting the swallowing capacity of the firstexpander while keeping the swallowing capacity of the second expanderconstant. In further embodiments, the temperature of the exhausttreatment device is adjusted by adjusting the swallowing capacity of thesecond expander while keeping the swallowing capacity of the firstexpander constant. As suggested above, the first and second expandersmay be of any suitable type, and they may be of the same type or ofdissimilar types. The first expander may be a piston expander with avariable valve actuation mechanism or a variable-geometry turbine. Thesecond expander may be a piston expander with a variable valve actuationmechanism or a variable-geometry turbine.

Preferably, the method comprises determining a temperature of theexhaust gases and, with an increasing exhaust gas temperature,decreasing the swallowing capacity of the first expander and increasingthe swallowing capacity of the second expander, and, with a decreasingexhaust gas temperature,increasing the swallowing capacity of the firstexpander and decreasing the swallowing capacity of the second expander.Thereby, an accurate temperature control may be provided.

According to another aspect of the invention, a method for an internalcombustion engine system is provided comprising a combustor arranged tocombust air and fuel, an expander arranged to receive, expand andextract energy from exhaust gases from the combustor, and to expel theexhaust gases from the expander by means of an expander exhaust valve,and an exhaust treatment device arranged to receive the expelled exhaustgases from the expander and to process the exhaust gases, the methodcomprising controlling the expander exhaust valve to control thetemperature of the process in the exhaust treatment device.

Said control of the expander exhaust valve may comprise controlling thetemperature of the process in the exhaust treatment device to be withinthe range of 300-450° C. The method provides an effective manner ofcontrolling the temperature of the exhaust treatment device, for keepingit within a range that is beneficial to the process therein. Thedistribution of exhaust treatment devices on both sides of the expander,as exemplified elsewhere herein, along with the control of the expanderexhaust valves, provides an advantageous way of adapting thetemperatures along the path of the exhaust gases for optimizing theprocesses in the exhaust treatment devices.

According to another aspect of the invention, a method for an internalcombustion engine system is provided comprising a combustor arranged tocombust air and fuel, an expander arranged to receive, expand andextract energy from exhaust gases from the combustor, the expandercomprising an inlet valve, and an exhaust treatment device arranged toreceive the exhaust gases from the expander and to process the exhaustgases, the method comprising injecting reductant for the exhausttreatment device upstream of the expander or into the expander,

-   controlling the expander inlet valve to allow exhaust gases into the    expander,-   wherein the timing and/or the duration of said reductant injection    is coordinated with said control of the expander inlet valve so as    for the reductant and the exhaust gases to mix in the expander.

It is understood that an injector may be arranged for said reductantinjection. The method will provide good mixing of the reductant with theexhaust gases. Said reductant injection is preferably provided so thatthe injected reductant flows past the open expander inlet valve.Preferably, the reductant injection is commenced simultaneously with orafter the opening of the expander inlet valve has commenced, and thereductant injection is terminated simultaneously with or before theclosing of the expander inlet valve has been finalized.

Further advantages and advantageous features of the invention aredisclosed in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

With reference to the appended drawings, below follows a more detaileddescription of embodiments of the invention cited as examples. In thedrawings:

FIG. 1 is a partially sectioned side view of a vehicle in the form of atruck.

FIG. 2 is a schematic perspective view of an engine system in thevehicle in FIG. 1.

FIG. 3 is a schematic cross-sectional view of the engine system in FIG.2.

FIG. 4 is a flow diagram depicting steps in a method carried out in thesystem in FIG. 3.

FIG. 5 is a flow diagram depicting steps in an alternative methodcarried out in the system in FIG. 3.

FIG. 6 is a schematic cross-sectional view of an engine system accordingto an alternative embodiment of the invention.

FIG. 7 is a schematic cross-sectional view of an engine system accordingto another alternative embodiment of the invention.

FIG. 8 is a schematic cross-sectional view of an engine system accordingto yet a further embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a vehicle in the form of a truck, or a tractor for asemitrailer. It should be noted however that the invention is applicableto a variety of alternative types of vehicles, such as a car, a bus, ora working machine such as a wheel loader. The vehicle comprises aninternal combustion engine system 1.

As can be seen in the schematic FIG. 2 the engine system 1 comprises amulti-stage compression and expansion internal combustion engine. Theengine comprises three combustors 3, in the form of cylinders withpistons, and three piston compressors 9. The system further comprises anair guide 901 arranged to guide compressed air from the compressors 9 tothe combustors 3. The air guide is provided with an air buffer container902, arranged to receive compressed air from the compressors 9, toprovide an air buffer volume for the compressed air, and to deliver thecompressed air to the combustors 3.

The system further comprises three first piston expanders 4 arranged toexpand exhaust gases from the combustors 3 and to extract energy fromthe expanded exhaust gases. An exhaust guide 701 is arranged to guideexhaust gases from the combustors 3 to the first expanders 4. Theexhaust guide 701 comprises a pre-expander exhaust treatment device 7described closer below.

The system further comprises a post-expander exhaust treatment device 6in the form of a selective catalytic reduction (SCR) catalyst. The SCRcatalyst 6 is arranged to receive exhaust gases from the first expander4 and to provide an exhaust treatment process to the received exhaustgases, which process reduces nitrogen oxides (NOx) as is known per se.Three second piston expanders 5 are arranged to receive and expandexhaust gases from the SCR catalyst 6 and to extract energy from theexpanded exhaust gases.

It is understood that the engine system may comprise any suitable numberof combustors 3, compressors 9, first expanders 4, and second expanders5. Herein, the engine is understood as comprising the combustors 3, thecompressors 9, the first expanders 4 and the second expenders 5, and theengine system is understood as comprising the engine, the pre-expanderexhaust treatment device 7, and the post-expander exhaust treatmentdevice 6.

Reference is made to FIG. 3 in which only one of the combustors 3, onlyone of compressors 9, and only one of the first expanders 4 are shown.The piston 301 of each combustor 3 is arranged to reciprocate in therespective cylinder 302, whereby the pistons are all arranged to drive acrankshaft 2 of the engine. For simplicity, the combustor 3, thecompressor 9, and the first expander 4 are shown as all being located inthe same cross-sectional plane; in a real implementation of theembodiment, the combustor 3, the compressor 9, and the first expander 4are preferably offset its relation to each other along the crankshaft 2.

The pistons 401 of the first expanders 4 are arranged to drive thecrankshaft 2 with the energy extracted from the exhaust gases from thecombustors 3. The pistons 501 of the second expanders 5 are arranged todrive the crankshaft 2 with the energy extracted from the exhaust gasesfroth the first expanders 4 and the SCR catalyst 6. Further, the pistons903 of the compressors 9 are all arranged to be driven by the crankshaft2.

The pre-expander exhaust treatment device 7 is arranged to provide anexhaust treatment process to the exhaust gases from the combustor 3. Thepre-expander exhaust treatment device 7 comprises an oxidation catalyst7, and a particulate filter 8 located downstream of the oxidationcatalyst 7.

The engine system comprises a control unit 15 arranged to controlvarious function of the system as described below.

The combustors 3 are provided with respective sets of combustor inletand outlet valves 303, 304, arranged to be actuated by a combustor valveactuator assembly 306. The outlet valve 304 is herein also referred toas an exhaust valve 304. The combustor valve actuator assembly 304 maybe arranged to actuate the combustor inlet and outlet valves 303, 304 inany manner known per se, e.g. with cams mounted on camshafts. Thecombustor valve actuator assembly 306 is controllable by the controlunit 15, to adjust the timing and the maximum movements of the combustorinlet and outlet valves 303, 304, in any manner known per se. Thecombustor valve actuator assembly 306 is herein also referred to as avariable valve actuation mechanism or a variable valve timing mechanism306.

In addition, the combustors 3 are provided with respective fuelinjectors 305 for injecting a fuel into the cylinders 302. The fuel maybe of any suitable type, e.g. diesel, methane e.g. in liquid natural gas(LNG), gasoline, etc. The fuel injectors 305 are controllable by thecontrol unit 15. In this example, the combustors 3 are arranged toprovide a Diesel cycle to extract work from the air and fuel provided.However, the invention is equally applicable to engines in which thecombustors are arranged to provide an Otto cycle, wherein the enginesystem may be provided with means for air mass flow control, such asvariable inlet and outlet valves 913, 914 of the compressors 9,described further below, for controlling the air supply to thecombustors 3. Alternatively, or in addition, the means for air mass flowcontrol may comprise one or, more throttles for controlling the airsupply to the combustors 3. The engine system may be provided with sparkplugs in the combustors.

The first expanders 4 are provided with respective sets of firstexpander inlet and outlet valves 403, 404, arranged to be actuated by afirst expander valve actuator assembly 406, including e.g. cams mountedon camshafts. The first expander valve actuator assembly 406 iscontrollable by the control unit 15, to adjust the timing and themaximum movements of the first expander inlet and outlet valves 403,404. The first expander valve actuator assembly 406 is herein alsoreferred to as a variable valve actuation mechanism or an expandervariable valve timing mechanism 406.

Similarly, the second expanders 5 are provided with respective sets ofsecond expander inlet and outlet valves 503, 504, arranged to beactuated by a second expander valve actuator assembly 506, includinge.g. cams mounted on camshafts. The second expander valve actuatorassembly 506 is controllable by the control unit 15, to adjust thetiming and the maximum movements of the second expander inlet and outletvalves 503, 504. The second expander valve actuator assembly 506 isherein also referred to as a variable valve actuation mechanism or anexpander variable valve timing mechanism.

In addition, the compressors 9 are provided with respective sets of saidcompressor inlet and outlet valves 913, 914, arranged to be actuated bya compressor valve actuator assembly 916, including e.g. cams mounted oncamshafts. The compressor valve actuator assembly 916 is controllable bythe control unit 15, to adjust the timing and the maximum movements ofthe compressor inlet and outlet valves 913, 914.

The system also comprises three injectors 8 arranged to inject reductantfor the SCR catalyst 6. Each injector 10 is arranged to inject thereductant downstream of the pre-expander exhaust treatment device 7,into a respective portion of the exhaust guide 701 leading to therespective first expander 4. The injectors 8 are controllable by thecontrol unit 15, to control the timing, the flow and the duration of theredundant injections. Specifically, the control unit 15 is arranged tocontrol the timing and duration of the reductant injections so that theyare coordinated with the actuations of the first expander inlet valves403, in order to enable good mixing of the reductant with the exhaustgases in the respective first expander 4. In some embodiments, eachinjector 8 is arranged to inject the reductant directly into therespective exhaust first expander 4.

In some embodiments, a single reductant injector may be provided, e.g.where the engine system is provided with a single first expander 4arranged to receive exhaust gases from a plurality of combustors 3. Thesingle reductant injector may be thereby be arranged to inject thereductant upstream of, or into the single first expander.

The control unit 15 is also arranged to receive signals from a mass airflow (MAF) sensor 141, located in an air intake system 921 locatedupstream of the compressors 9 and arranged to guide air to thecompressors 9. The control unit 15 is arranged to determine the load ofthe engine during its operation in the vehicle, as is known per se, e.g.based on signals from the MAF sensor 702, an accelerator pedal position(APP) sensor, (not shown), indicating a requested torque for the engine,and/or a manifold absolute pressure (MAP) sensor (not shown) in the airintake system 921. The load of the engine may also be based on therotational speed of the engine.

The control unit 15 is further arranged to receive signals from a firsttemperature sensor 142, arranged at the pre-expander exhaust treatmentdevice 7. The control unit 15 is arranged to determine the temperaturein the pre-expander exhaust treatment device 7, based on signals fromthe first temperature sensor 142.

The control unit 15 is also arranged to receive signals from a secondtemperature sensor 143, arranged at the post-expander exhaust treatmentdevice 6. The control unit 15 is arranged to determine the temperaturein the post-expander exhaust treatment device 6, based on signals fromthe second temperature sensor 143.

Reference is made to FIG. 4 depicting steps in a method carried out inthe system described above. During operation of the engine system in thevehicle, the control unit 15 determines S1 the load of the enginesystem, as described above.

The method involves controlling the injector 8, to inject S4 redundantupstream of the first expander for the post-expander exhaust treatmentdevice. The timing and duration of the reductant injections arecoordinated with the actuations of the first expander inlet valve 403,in order to enable good mixing of the reductant with the exhaust gasesin the expander.

The method also involves controlling the temperature of the process inthe post-expander exhaust treatment device 6. During, operation of theengine system in the vehicle, the control unit 15 determines S5 thetemperature of the post-expander exhaust treatment device 6, asdescribed above.

The method comprises comparing S501 the temperature of the post-expanderexhaust treatment device 6 with a target temperature of thepost-expander exhaust treatment device 6. The target temperature may bepredetermined; it may be a fixed value or a value determined independence on one or more operational parameters of the engine system.

If the determined temperature is below the target temperature, the firstexpander variable valve actuation mechanism 406 is adjusted S502 so asto delay, in the cycles of the first expander, a closing event of thefirst expander inlet valve 403, and the second expander variable valveactuation mechanism 506 is adjusted so as to advance, in the cycles ofthe second expander, a closing event of the second expander inlet valve503. Thereby the swallowing capacity of the first expander is increasedand the swallowing capacity of the second expander is decreased. Therebythe pressure and the temperature between the first and second expanderswill be increased, whereby the temperature of the post-expander exhausttreatment device 6 will be increased.

If the determined temperature is above the target temperature, the firstexpander variable valve actuation mechanism 406 is adjusted S503 so asto advance, in the cycles of the first expander, the closing event ofthe first expander inlet valve 403, and the second expander variablevalve actuation mechanism 506 is adjusted so as to delay, in the cyclesof the second expander, the closing event of the second expander inletvalve 503. Thereby the swallowing capacity of the first expander isdecreased and the swallowing capacity of the second expander isincreased. Thereby the pressure and the temperature between the firstand second expanders will be decreased, whereby the temperature of thepost-expander exhaust treatment device 6 will be decreased.

Upon adjusting the first and second expander inlet valve closingtimings, the first and second expander variable valve actuationmechanisms 406, 506 are controlled so as to adjust S504 the first andsecond expander exhaust valves 404, 504 to minimize the pressuredifference across the expander exhaust valves 404, 504 at the openingevents of the expander exhaust valves.

Further the first and second expander exhaust valves 404, 504 areadjusted to minimize the pressure difference across the expander inletvalves 403, 503 at opening events of the expander inlet valves; this isdone by adjusting the timing of the expander exhaust valve closingevents, thereby controlling the degree of recompression in the first andsecond expanders.

In alternative embodiments, instead of determining the post-expanderexhaust treatment device temperature, the temperature of the exhaustgases may be determined, and the swallowing capacities of the first andsecond expanders may be adjusted based on the determined exhaust gastemperature.

Reference is made to FIG. 5 depicting steps in a further method carriedout in the system described above. During an operation of the enginesystem 1, the air guide 901 may present a pressure within the range of8-12 bar and a temperature within the range of 250-350° C. The methodinvolves controlling the temperature of the process in the pre-expanderexhaust treatment device 7. During operation of the engine system in thevehicle, the control unit 15 determines S1 the load of the enginesystem, as described above.

The method involves, as in the example described with reference to FIG.4, controlling the injector 8, to inject S4 redundant upstream of thefirst expander for the post-expander exhaust treatment device. Thetiming and duration of the reductant injections are coordinated with theactuations of the first expander inlet valve 403, in order to enablegood mixing of the reductant with the exhaust gases in the expander.

The method also involves controlling the temperature of the process inthe post-expander exhaust treatment device 6. During operation of theengine system in the vehicle, e.g. during a cold start event of theengine system, the control unit 15 determines 55 the temperature of thepost-expander exhaust treatment device 6, as described above.

Based on the determined post-expander exhaust treatment devicetemperature, and optionally the engine load, the first expander outletvalves 404 are controlled S6 in the first expander cycles so as tocontrol the post-expander exhaust treatment device temperature. Morespecifically, by opening the first expander outlet valves 404 relativelyearly in the cycles, the expansion ratio of the first expanders 4 willbe reduced, and some heat is distributed from providing power for thefirst expander crankshaft drive to providing heat to the post-expanderexhaust treatment device 6. Thereby, the temperature of thepost-expander exhaust treatment device 6 may be increased. Also, energynot absorbed by the first expanders 4 due to the reduced expansionratio, may be absorbed by the second expanders 5. By opening the firstexpander outlet valves 404 relatively late in the cycles, the heatescape from the first expanders 4 may be reduced, whereby thetemperature of the post-expander exhaust treatment device 6 may bedecreased.

During the engine system operation, the controller 14 periodicallyrepeats said steps of engine load determination S1, reductant injectionS4, post-expander exhaust treatment device temperature determination S5,and first expander outlet valve control S6.

In the configuration described above with an oxidation catalyst 10 and aparticulate filter 11, the pre-expander exhaust treatment device 7suitably presents a temperature within the range of 550-800° C. and apressure within the range of 10-25 bar. The methods described withreference to FIG. 4 and FIG. 5 provide effective manners of controllingthe temperature of the post-expander exhaust treatment device 6, forkeeping it within a range that is beneficial to the processes therein.In the configuration described above with an SCR catalyst, thepost-expander exhaust treatment device 6 suitably presents a temperaturewithin the range of 300-450° C. More generally, the methods provide anadvantageous distribution and control of the temperatures along the pathof the exhaust gases, so that exhaust treatment devices distributedalong said path are provided with different temperatures which are eachoptimized for the respective exhaust treatment device.

In this example, the compressor 9 may be arranged to compress the air toa volumetric ratio of 1:1-1:8, preferably 1:4-1:6, in dependence on theactuation of the variable compressor inlet and outlet valves 913, 914.The combustors 3 may be arranged to compress the air from thecompressors to a ratio of 1:8-1:14, preferably 1:10-1:12, and to expandthe gases in the combustors 3 by a ratio of 1:4-1:14, preferably1:10-1:12, in dependence on the actuation of the variable combustorinlet and outlet valves 303, 304. The first expander 4 may be arrangedto expand the exhaust gases with a ratio of 1:2-1:6, preferably 1:3-1:4,and the second expander 5 may be arranged to expand the exhaust gaseswith a ratio of 1:2-1:6, preferably 1:2-1:3, in dependence on theactuation of the variable first and second expander inlet and outletvalves 403, 404, 503, 504. Specifically, as suggested, the firstexpander expansion ratio may be adjusted to control the temperature ofthe post-expander exhaust treatment device 6. It should be noted that inembodiments of the invention, any of the compression and expansionratios may be outside the intervals mentioned above.

Reference is made to FIG. 6, showing an engine system according to analternative embodiment of the invention. This embodiment shares featureswith the embodiment described with reference to FIG. 2-FIG. 5. However,some further advantageous features are also provided.

In the embodiment in FIG. 6, each pair of a second expander 5 and acompressor 9 are integrated so as to share a piston 591 which isconnected to the crankshaft 2. Thus, the compressors 9 and the secondexpanders 5 form three compressor and expander combinations 5, 9, inwhich the pistons 591 is arranged to reciprocate in shared cylinders592.

In FIG. 6 one of the compressor and expander combinations 5, 9 is shown.The compressor and expander combination 5, 9, herein also referred to asa combined compressor and expander 5, 9, presents on a first side of thepiston 591 a first head 595, and compressor inlet and outlet valves 913,914, arranged to be actuated by a compressor valve actuator assembly,(not shown), similarly to the compressor inlet and outlet valves 913,914 in the embodiment in FIG. 3. The compressor and expander combination5, 9 also presents on a second side of the piston 591 a second head 596,and second expander inlet and outlet valves 503, 504, arranged to beactuated by a second expander valve actuator assembly, (not shown),similarly to the second expander inlet and outlet valves 913, 914 in theembodiment in FIG. 3.

The piston is connected to the crankshaft 2 via a connecting rod 593 andan extension rod 594. The extension rod connects the piston 591 with theconnecting rod 593, and extends with a tight fit through an opening inthe second head 596. Said tight fit may be accomplished, e.g. with asuitable arrangement of a sliding bush or piston rings.

The compressor and expander combination 5, 9 is arranged to admit, byactuation of the compressor inlet valve 913, air to the shared cylinder592, on the first side of the piston 591. The compressor and expandercombination 5, 9 is further arranged to compress the air by the pistonmovement caused by the crankshaft rotation. The compressor and expandercombination 5, 9 is further adapted to admit, by actuation of the secondexpander inlet valve 503, exhaust gases, received from the firstexpander 4 and the post-expander exhaust treatment device 6, on thesecond side of the piston 591. The compressor and expander combination5, 9 is arranged to expand the admitted exhaust gases, thereby urgingthe piston 591 towards the fast heat 595.

By the urge of the piston 591 towards the first heat 595, in addition todriving the crankshaft 2, the compressor and expander combination 5, 9is arranged to deliver energy for the air compression in a directmanner. More specifically, the exhaust gases provides a direct pressureon the shared piston 591 in turn serving to directly exert a directpressure on the air. Thereby, mechanical losses for the transfer of thisenergy is substantially eliminated. Also, compared to providing thecompressor and expander separately, the compressor and expandercombination 5, 9 results in a reduced number of parts, since the piston591 and the cylinder 592 are shared, thereby reducing the complexity andcost of the engine system 1.

It should be noted that in alternative embodiments, the compressor 9 andthe first expander 4 may be integrated so as to share a piston which isconnected to the crankshaft 2, similarly to what is described withreference to FIG. 6.

It should be noted that while the inlet and outlet valves 303, 304, 403,404, 503, 504, 913, 914 in the drawings are depicted as poppet valves,any one of them may be provided in any suitable alternative form, suchas a sleeve valve.

Reference is made to FIG. 7, showing an engine system according to afurther alternative embodiment of the invention. This embodiment sharesfeatures with the embodiment described with reference to FIG. 2-FIG. 5.However, some further advantageous features are also provided.

In FIG. 3, the pistons of the compressors 9, the first expanders 4, andthe second expanders 5 are indirectly connected to the crankshaft 2.However, the invention is applicable also to engine systems, wherepistons of the compressors 9 and the first expanders 4 are indirectly,connected to the crankshaft 2, via an additional crankshaft 2 b and achain or belt connection 201, as shown in FIG. 7. In FIG. 7, the pistonsof the compressors 9 and the first expanders 4 are directly connected tothe additional crankshaft 2 b, and the chain or belt connection 201 isprovided between the crankshafts 2, 2 b. Any suitable type of connectionbetween the crankshafts 2, 2 b may be provided. For example, as analternative to the chain or belt connection 201, a toothed gear wheelconnection between the crankshafts 2, 2 b may be provided.

In should be noted that in the embodiment in FIG. 7, the second expander5 comprises a piston arranged to drive a further crankshaft 2 cconnected to the additional crankshaft 2 b, via a further chain or beltconnection 202. The system also comprises an additional compressor 19with a piston connected to the further crankshaft 2 c. The additionalcompressor 19 is located upstream of the piston compressor 9, and isarranged to provide an additional compression step.

Reference is made to FIG. 8, showing an engine system according to yetanother embodiment of the invention. This embodiment shares featureswith the embodiment described with reference to FIG. 7. However, in theembodiment in FIG. 8, the second expander 5 comprises a turbine arrangedto drive an additional compressor 19. The additional compressor 19 isprovided in the form of a centrifugal compressor 19, which is directlyconnected by means of a shaft to the turbine of the second expander. Theadditional compressor is located upstream of the piston compressor 9,and is arranged to provide an additional compression step.

It is to be understood that the present invention is not limited to theembodiments described above and illustrated in the drawings; rather, theskilled person will recognize that many changes and modifications may bemade within the scope of the appended claims.

The invention claimed is:
 1. An internal combustion engine system comprising an internal combustion engine comprising at least one combustor, and a first expander arranged to receive exhaust gases from at least one of the at least one combustor, and to expand and extract energy from the exhaust gases, wherein the engine comprises a crankshaft, and the combustor comprises a piston arranged to reciprocate in a cylinder, and to drive the crankshaft, wherein the first expander is a piston expander arranged to drive the crankshaft with the extracted energy, wherein the engine comprises a second expander arranged to receive exhaust gases from the first expander, and to expand and extract energy from the exhaust gases, wherein the system comprises an exhaust treatment device arranged to receive exhaust gases from the first expander, to process the received exhaust gases, and to deliver the processed exhaust gases to the second expander, and, where the first expander is a piston expander, the first expander comprises an expander inlet valve and/or an expander exhaust valve, the engine further comprising an expander variable valve timing mechanism arranged to actuate the expander inlet valve and/or an expander variable valve timing mechanism arranged to actuate the expander exhaust valve, wherein the system further comprises a control unit configured to: receive a signal indicative of a temperature in the exhaust treatment device; and control the valve timing of the expander exhaust valve based on the temperature in the exhaust treatment device.
 2. A system according to claim 1, wherein the exhaust treatment device is a selective catalytic reduction (SCR) catalyst.
 3. A system according to claim 1, wherein the system comprises an injector arranged to inject reductant for the exhaust treatment device, upstream of the first expander or into the first expander.
 4. A system according to claim 3, wherein the injector is arranged to inject reductant into the first expander and onto a piston of the first expander.
 5. A system according to claim 1, wherein the system is arranged so that during an operation thereof, the exhaust treatment device presents a temperature within the range of 300-450.degree. C.
 6. A system according to claim 1, wherein the system comprises in addition to the exhaust treatment device a pre-expander exhaust treatment device arranged to receive exhaust gases from the combustor, to provide an exhaust treatment process to the exhaust gases, and to deliver processed exhaust gases to the first expander.
 7. A system according to claim 6, wherein the pre-expander exhaust treatment device comprises an oxidation catalyst.
 8. A system according to claim 6, wherein the pre-expander exhaust treatment device comprises a particulate filter.
 9. A system according to claim 7, wherein the pre-expander exhaust treatment device comprises a particulate filter and the particulate filter is located downstream of the oxidation catalyst.
 10. A system according to claim 6, wherein the system is arranged so that during an operation thereof, the pre-expander exhaust treatment device presents a temperature within the range of 550-1300.degree. C.
 11. A system according to claim 1, wherein the system comprises a crankshaft, and that the combustor comprises a piston arranged to reciprocate in a cylinder, and to drive the crankshaft.
 12. A system according to claim 1, wherein the system comprises a crankshaft, and that the first expander is arranged to drive the crankshaft with the extracted energy.
 13. A system according to claim 1, wherein the second expander is a piston expander.
 14. A system according to claim 1, wherein the system comprises a crankshaft, and that the second expander is arranged to drive the crankshaft with the extracted energy.
 15. A system according to claim 1, wherein the combustor comprises an exhaust valve, the system further comprising a variable valve timing mechanism arranged to actuate the exhaust valve.
 16. A system according to claim 1, wherein the first expander comprises a hydrolysing reactor.
 17. A vehicle provided with an internal combustion engine system according to claim
 1. 